Airfoil tip geometry to reduce blade wear in gas turbine engines

ABSTRACT

An airfoil for use in a turbomachine includes a pressure sidewall and a suction sidewall coupled to the pressure sidewall. The suction sidewall and the pressure sidewall define a leading edge and an opposite trailing edge. The leading edge and the trailing edge define a chord distance. The airfoil further includes a root portion, and a tip portion. The tip portion extends between the pressure sidewall and the suction sidewall such that the tip portion is substantially perpendicular to each sidewall. The tip portion includes at least one planar section and at least one oblique section that forms a recess within the tip portion. The at least one oblique section extends from the at least one planar section towards the root portion along the chord distance. The tip portion is configured to reduce airfoil wear during contact with a surrounding casing.

BACKGROUND

The field of the disclosure relates generally to gas turbine enginesand, more particularly, to airfoil tip geometry to reduce blade wear ingas turbine engines.

At least some known turbomachines, i.e., gas turbine engines, include acompressor that compresses air through a plurality of rotatablecompressor blades enclosed within a compressor casing, and a combustorthat ignites a fuel-air mixture to generate combustion gases. Thecombustion gases are channeled through rotatable turbine blades in aturbine through a hot gas path. Such known turbomachines convert thermalenergy of the combustion gas stream to mechanical energy used togenerate thrust and/or rotate a turbine shaft to power an aircraft.Output from the turbomachine may also be used to power a machine, suchas, an electric generator, a compressor, or a pump.

Under some known operating conditions, rub events occur within theturbomachine, wherein a rotor blade tip contacts or rubs against thesurrounding stationary casing inducing radial and tangential loads intoa rotor blade airfoil. Generally during rub events, these loads causethe rotor blade to vibrate and deflect causing wear thereto. Excessivetip rub events cause wear to the rotor blade including, but not limitedto, loss of blade material, which decreases turbomachine performance.

During tip rub events, the rotor blade is known to lose more materialfrom the tip than the penetration distance into the casing. For example,if the blade tip penetrates the casing 1 mil (25.4 micrometers (μm))then the blade tip is known to lose as much as 10 mils (254 μm) ofmaterial. The thickness of material lost in the blade tip divided by thepenetration distance into the casing is known as a rub ratio. In theabove example, the rub ratio would be 10:1, or known to have a rub ratiovalue of 10. Turbomachines with a high rub ratio are known to havedecreased performance and decreased service life resulting in highermaintenance costs.

BRIEF DESCRIPTION

In one aspect, an airfoil for use in a turbomachine is provided. Theairfoil includes a pressure sidewall and a suction sidewall coupled tothe pressure sidewall, the suction sidewall and the pressure sidewalldefine a leading edge and an opposite trailing edge. The leading edgeand the trailing edge define a chord distance. The airfoil furtherincludes a root portion, and a tip portion. The tip portion extendsbetween the pressure sidewall and the suction sidewall such that the tipportion is substantially perpendicular to each sidewall. The tip portionincludes at least one planar section and at least one oblique sectionthat forms a recess within the tip portion. The at least one obliquesection extends from the at least one planar section towards the rootportion to along the chord distance. The tip portion is configured toreduce airfoil wear during contact with a surrounding casing.

In a further aspect, a turbomachine is provided. The turbomachineincludes a casing, and a rotor assembly, the casing at least partiallyextending about the rotor assembly. The rotor assembly includes a rotorshaft, and a plurality of rotor blades coupled to the rotor shaft. Eachrotor blade of the plurality of rotor blades includes an airfoilincluding a pressure sidewall and a suction sidewall coupled to thepressure sidewall. The suction sidewall and the pressure sidewall definea leading edge and an opposite trailing edge. The leading edge and thetrailing edge define a chord distance. The airfoil further includes aroot portion, and a tip portion. The tip portion extends between thepressure sidewall and the suction sidewall such that the tip portion issubstantially perpendicular to each sidewall. The tip portion includesat least one planar section and at least one oblique section that formsa recess within said tip portion. The at least one oblique sectionslopes from the at least one planar section towards the root portionalong the chord distance. The tip portion is configured to reduce rotorblade wear during contact with the casing.

In another aspect, a method for reducing blade wear during turbomachineoperation is provided. The turbomachine includes a casing, a rotorshaft, and a plurality of rotor blades. Each rotor blade of theplurality of rotor blades includes an airfoil including a pressuresidewall and a suction sidewall coupled to the pressure sidewall. Thesuction sidewall and the pressure sidewall define a leading edge and anopposite trailing edge. The leading edge and the trailing edge define achord distance. The airfoil further includes a root portion, and a tipportion. The tip portion extends between the pressure sidewall and thesuction sidewall such that the tip portion is substantiallyperpendicular to each sidewall. The method includes removing bladematerial from the tip portion including forming a recess from at leastone oblique section adjacent to at least one planar section on the tipportion. The at least one oblique section extends from the at least oneplanar section towards the root portion along the chord distance. Themethod further includes coupling the rotor blade to the rotor shaft suchthat during turbomachine operation, when the tip portion contacts thecasing, wear of the rotor blade is reduced.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic diagram of an exemplary turbomachine, i.e., aturbofan;

FIG. 2 is a perspective view of an exemplary rotor blade that may beused within the turbomachine shown in FIG. 1;

FIG. 3 is a schematic view of an exemplary tip portion of the rotorblade shown in FIG. 2;

FIG. 4 is a graphical view of operational features of the tip portionshown in FIG. 3;

FIG. 5 is a schematic view of an alternative tip portion that may beused with the rotor blade shown in FIG. 2;

FIG. 6 is a schematic view of another alternative tip portion that maybe used with the rotor blade shown in FIG. 2; and

FIG. 7 is a schematic view of a further alternative tip portion that maybe used with the rotor blade shown in FIG. 2.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems comprisingone or more embodiments of this disclosure. As such, the drawings arenot meant to include all conventional features known by those ofordinary skill in the art to be required for the practice of theembodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and claims, reference will be made to anumber of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, “approximately”, and “substantially”, are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged, such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

Rotor blade tip geometries as described herein provide a method forreducing blade wear in a turbomachine. Specifically, a rotor bladeincludes an airfoil having a suction sidewall coupled to a pressuresidewall at a leading edge and a trailing edge. A tip portion extendsbetween the suction sidewall and the pressure sidewall and includes aplanar section and an oblique section. In some embodiments, the tipportion includes a first oblique section and a second oblique section.Modifying the rotor blade tip geometry by grinding the tip portion andforming the oblique section reduces the rub ratio of the rotor blade,and thereby, the wear of the rotor blade. Specifically, the obliquesection is sized such that a contact area between the rotor blade and asurrounding casing is reduced, thereby decreasing the radial andtangential loads induced into the rotor blade during a rub event.Reducing the loads resulting from a rub event decreases vibration anddeflection of the rotor blade and reduces material loss at the tipportion. Furthermore, modifying the rotor blade tip geometry changes thevibratory modes of the rotor blade such that radial elongation isdecreased further reducing material loss at the tip portion.Additionally, a reduction in radial deflection allows the rotor blade tobe positioned closer to the surrounding casing. Accordingly, decreasingthe rub ratio of the rotor blade decreases wear and material loss duringa rub event, increases turbomachine performance, and reduces maintenancecosts.

As used herein, the terms “axial”, and “axially”, refer to directionsand orientations which extend substantially parallel to a centerline138, as shown in FIG. 1, of a turbine engine. Moreover, the terms“radial”, and “radially”, refer to directions and orientations whichextend substantially perpendicular to centerline 138 of the turbineengine. In addition, as used herein, the terms “circumferential”, and“circumferentially”, refer to directions and orientations which extendarcuately about centerline 138 of the turbine engine. The term “fluid”,as used herein, includes any medium or material that flows, including,but not limited to, air.

FIG. 1 is a schematic view of a turbomachine 100, i.e., a gas turbineengine, and more specifically, an aircraft engine or turbofan. In theexemplary embodiment, turbomachine 100 includes an air intake section102, and a compressor section 104 that is coupled downstream from, andin flow communication with, intake section 102. Compressor section 104is enclosed within a compressor casing 106. A combustor section 108 iscoupled downstream from, and in flow communication with, compressorsection 104, and a turbine section 110 is coupled downstream from, andin flow communication with, combustor section 108. Turbine section 110is enclosed within a turbine casing 112 and includes an exhaust section114 that is downstream from turbine section 110. A combustor housing 116extends about combustor section 108 and is coupled to compressor casing106 and turbine casing 112. Moreover, in the exemplary embodiment,turbine section 110 is coupled to compressor section 104 through a rotorassembly 118 that includes, without limitation, a compressor rotor, ordrive shaft 120 and a turbine rotor, or drive shaft 122.

In the exemplary embodiment, combustor section 108 includes a pluralityof combustor assemblies, i.e., combustors 124 that are each coupled inflow communication with compressor section 104. Combustor section 108also includes at least one fuel nozzle assembly 126. Each combustor 108is in flow communication with at least one fuel nozzle assembly 126.Moreover, in the exemplary embodiment, turbine section 110 andcompressor section 104 are rotatably coupled to a fan assembly 128through drive shaft 120. Alternatively, turbomachine 100 may be a gasturbine engine and for example, and without limitation, be rotatablycoupled to an electrical generator and/or a mechanical driveapplication, e.g., a pump. In the exemplary embodiment, compressorsection 104 includes at least one compressor stage that includes acompressor blade assembly 130 and an adjacent stationary stator vaneassembly 132. Each compressor blade assembly 130 includes a plurality ofcircumferentially spaced blades (not shown) and is coupled to rotorassembly 118, or, more specifically, compressor drive shaft 120. Eachstator vane assembly 132 includes a plurality of circumferentiallyspaced stator vanes (not shown) and is coupled to compressor casing 106.Also, in the exemplary embodiment, turbine section 110 includes at leastone turbine blade assembly 134 and at least one adjacent stationarynozzle assembly 136. Each turbine blade assembly 134 is coupled to rotorassembly 118, or, more specifically, turbine drive shaft 122 along acenterline 138.

In operation, air intake section 102 channels air 140 towards compressorsection 104. Compressor section 104 compresses air 140 to higherpressures and temperatures prior to discharging compressed air 142towards combustor section 108. Compressed air 142 is channeled to fuelnozzle assembly 126, mixed with fuel (not shown), and burned within eachcombustor 124 to generate combustion gases 144 that are channeleddownstream towards turbine section 110. After impinging turbine bladeassembly 134, thermal energy is converted to mechanical rotationalenergy that is used to drive rotor assembly 118. Turbine section 110drives compressor section 104 and/or fan assembly 128 through driveshafts 120 and 122, and exhaust gases 146 are discharged through exhaustsection 114 to the ambient atmosphere.

FIG. 2 is a perspective view of an exemplary rotor blade 200, and morespecifically, a compressor blade, that may be found within turbomachine100 (shown in FIG. 1). In the exemplary embodiment, rotor blade 200includes an airfoil 202, a platform 204, and a dovetail 206 that is usedfor mounting rotor blade 200 to compressor drive shaft 120 (shown inFIG. 1). Airfoil 202 includes a root portion 208, adjacent platform 204,and an opposite tip portion 210. Further, airfoil 202 includes apressure sidewall 212 and an opposite suction sidewall 214. In theexemplary embodiment, pressure sidewall 212 is substantially concave andsuction sidewall 214 is substantially convex. Pressure sidewall 212 iscoupled to suction sidewall 214 at a leading edge 216 and at an axiallyspaced trailing edge 218. Trailing edge 218 is spaced chord-wise anddownstream from leading edge 216. Pressure sidewall 212 and suctionsidewall 214 each extend longitudinally or radially outward in a length220 from root portion 208 to blade tip portion 210. Along a chord ofblade 200, a mid-chord line 217 is defined at the mid-point of thechord. Tip portion 210 is defined between sidewalls 212 and 214 andincludes a planar section 222 that is defined as the radially outersurface of blade 200 and substantially perpendicular to each sidewall212 and 214. Tip portion 210 also includes an oblique section 300adjacent to planar section 222 and described further below in referenceto FIG. 3. In an alternative embodiment, rotor blade 200 may have anyother configuration that enables turbomachine to function as describedherein.

In the exemplary embodiment, compressor casing 106 circumferentiallyextends around rotor blade 200, and tip portion 210. Specifically, tipportion 210 at leading edge 216 and oblique section 300 has a gapdistance 224 that is substantially not equal to a gap distance 226 oftip portion 210 at trailing edge 218 and planar section 222.Furthermore, a flow path 228 for compressed air 142 (shown in FIG. 1) isdefined between compressor casing 106 and shaft 120.

During operation, rotor blade 200 rotates within casing 106 aboutcenterline 138 (shown in FIG. 1). In some operating conditions, such asan imbalanced load, rotor blade 200, specifically tip portion 210,contacts or rubs against casing 106, which is also known as a rub event.Specifically, tip portion 210 is jammed into casing 106, such thatradial and tangential loads are induced into rotor blade 200. Generallyduring rub events, these loads cause rotor blade 200 to vibrate anddeflect causing wear thereto. The deflection of rotor blade 200, atleast in part, depends on the vibratory modes of the blade that areexcited during the rub event. Some vibratory modes are known to increaseradial elongation of rotor blade 200 resulting in an increased amount ofwear to tip portion 210.

At least some of the wear rotor blade 200 incurs during the rub eventincludes material loss from tip portion 210. Specifically, when tipportion 210 contacts casing 106, rotor blade 200 loses material at tipportion 210 such that overall length 220 is reduced. A rub ratio is avalue that may be used to quantify the amount of wear rotor blade 200experiences during the rub event. A rub ratio is defined as a thicknessof material lost from tip portion 210 during a rub event divided by anamount of penetration by tip portion 210 into casing 106. For example,if tip portion 210 penetrates into the casing 1 mil (25 μm) and 10 mils(101 μm) of blade material is lost from tip portion 210, the rub ratiois 10.

FIG. 3 is a schematic view of an exemplary tip portion 210 for use withrotor blade 200. In the exemplary embodiment, tip portion 210 includesplanar section 222 that extends from pressure sidewall 212 to suctionsidewall 214 and substantially perpendicular thereto. Additionally, tipportion 210 includes an oblique section 300 that slopes from planarsection 222 inwards towards root portion 208 to leading edge 216 forminga recess 301. Oblique section 300 also extends from pressure sidewall212 to suction sidewall 214 and is substantially perpendicular thereto.In the exemplary embodiment, oblique section 300 extends a distance 302along tip portion 210. Specifically, oblique section 300 extends alongtip portion 210 from leading edge 216 within a range from approximately5% to approximately 50% of a chord distance 304 of airfoil 202. Forexample, oblique section 300 extends along tip portion 210 from leadingedge 216 within a range from approximately 5% to approximately 15% of achord distance 304 of airfoil 202. More specifically, in the illustratedembodiment, oblique section 300 extends along tip portion 210 fromleading edge 216 approximately 15% of chord distance 304. Obliquesection 300 also has a depth 306 from planar section 222 such that alength 308 of leading edge 216 that extends from tip portion 210 to rootportion 208 is shorter than a length 310 of trailing edge 218 from tipportion 210 to root portion 208. Said another way, distance 224 (shownin FIG. 2) between casing 106 (shown in FIG. 2) and leading edge 216 isgreater than distance 226 (shown in FIG. 2) between casing 106 andtrailing edge 218. In the exemplary embodiment, depth 306 is within arange including approximately 2 mils (51 μm) to approximately 5 mils(127 μm). In alternative embodiments, depth 306 may have any otherdistance that enables tip portion 210 to function as described herein.

In some embodiments, for example, oblique section 300 is formed at line312 that extends a distance 314 along tip portion 210 from leading edge216 within a range from approximately 15% to approximately 30% of chorddistance 304 forming recess 301. Specifically, in the illustratedembodiment, oblique section line 312 extends approximately 30% of chorddistance 304 from leading edge 216. Extending recess 301 further fromleading edge 216, such as with oblique section line 312, reduces thearea of planar section 222 that contacts with casing 106 during a rubevent thereby lowering the contact force between rotor blade 200 andcasing 106. In other embodiments, for example, oblique section 300 isformed at line 316 that extends a distance 318 along tip portion 210from leading edge 216 within a range from approximately 30% toapproximately 50% of chord distance 304 forming recess 301.Specifically, in the illustrated embodiment, oblique section line 316extends approximately 50% of chord distance 304 from leading edge 216.Extending recess 301 further from leading edge 216, such as with obliquesection line 316, further reduces the area of planar section 222 thatcontacts with casing 106 during a rub event thereby lowering the contactforce between rotor blade 200 and casing 106. In further embodiments,oblique section 300 may extend any other distance along tip portion 210from leading edge 216 that enables tip portion 210 to function asdescribed herein.

Additionally, in some embodiments, an oblique section 320 is definedfrom trailing edge 218 such that a length of trailing edge 218 from tipportion 210 to root portion 208 is shorter than a length of leading edgefrom tip portion 210 to root portion 208. Said another way, distance 226between casing 106 and trailing edge 218 is greater than distance 224between casing 106 and leading edge 216. In the exemplary embodiment,oblique section 320 extends along tip portion 210 from trailing edge 218within a range from approximately 5% to approximately 50% of chorddistance 304 of airfoil 202. For example, oblique section 320 extends adistance 322 from trailing edge 218 within a range from approximately 5%to approximately 15% of chord distance 304 forming a recess 321.Specifically, in the illustrated embodiment, oblique section 320 extendsapproximately 15% of chord distance 304 from trailing edge 218. In otherembodiments, for example, oblique section 320 is formed at line 324 thatextends a distance 326 from trailing edge 218 within a range fromapproximately 15% to approximately 30% of chord distance 304 formingrecess 321. Specifically, in the illustrated embodiment, oblique sectionline 324 extends approximately 30% of chord distance 304 from trailingedge 218. Extending recess 321 further from trailing edge 216, such aswith oblique section line 324, reduces the area of planar section 222that contacts with casing 106 during a rub event thereby lowering thecontact force between rotor blade 200 and casing 106. In yet otherembodiments, for example, oblique section 320 is formed at line 328 thatextends a distance 330 from trailing edge 218 within a range fromapproximately 30% to approximately 50% of chord distance 304 formingrecess 321. Specifically, in the illustrated embodiment, oblique sectionline 328 extends approximately 50% of chord distance 304 from trailingedge 218. Extending recess 321 further from trailing edge 218, such aswith oblique section line 328, reduces the area of planar section 222that contacts with casing 106 during a rub event thereby lowering thecontact force between rotor blade 200 and casing 106. In alternativeembodiments, oblique section 320 extends any other distance along tipportion 210 from trailing edge 218 that enables tip portion 210 tofunction as described herein.

Furthermore, in some embodiments, tip portion 210 includes obliquesections on both leading edge 216 and trailing edge 218. For example,tip portion 210 includes oblique section 300 and oblique section 320such that a length of leading edge 216 from tip portion 210 to rootportion 208 is substantially equal to a length of trailing edge 218 fromtip portion 210 to root portion 208. Said another way, distance 224between casing 106 and leading edge 216 is substantially equal todistance 226 between casing 106 and trailing edge 218.

In the exemplary embodiment, oblique section 300 is formed by grindingtip portion 210 and removing rotor blade 200 material in a machine shopusing known machining techniques. Alternatively, oblique section 300 canbe formed by any other method that enables rotor blade 200 to functionas described herein.

FIG. 4 is a graphical view, i.e., chart 400, of operational features oftip portion 210 shown in FIGS. 2-3. Specifically, chart 400 illustratesa rub ratio value for four different tip geometries of tip portion 210(shown in FIG. 3). The rub ratio is defined as a thickness of materiallost from tip portion 210 during a rub event divided by an amount ofpenetration by tip portion 210 into casing 106 as described in referenceto FIG. 2. Chart 400 includes a y-axis 402 defining the rub ratio valueon a linear scale. Along the x-axis, four different tip geometries areshown: a baseline geometry 404, which includes planar section 222 (shownin FIG. 3) that extends the full length of tip portion 210 from leadingedge 216 (shown in FIG. 3) to trailing edge 218 (shown in FIG. 3); afirst geometry 406, which includes oblique section 300 (shown in FIG. 3)adjacent to leading edge 216; a second geometry 408, which includesoblique section 320 (shown in FIG. 3) adjacent to trailing edge 218; anda third geometry 410, which includes both oblique sections 300 and 320.

In the exemplary chart 400, each tip geometry 404, 406, 408, and 410 issubjected to a rub event with casing 106 (shown in FIG. 1) and athickness of material loss at each of leading edge 216, mid-chord line217 (shown in FIG. 3), and trailing edge 218 are recorded. Then the rubratio at each leading edge 216, mid-chord line 217, and trailing edge218 are determined. Chart 400 includes a first group of bars 412 thatrepresents the rub ratio for tip portion 210 with baseline geometry 404.A leftmost bar 414 represents the rub ratio at leading edge 216 ofbaseline geometry 404, a middle bar 416 represents the rub ratio atmid-chord line 217, and a rightmost bar 418 represents the rub ratio attrailing edge 218.

Further, in the exemplary chart 400, a second group of bars 420represents the rub ratio for tip portion 210 with first tip geometry406. A leftmost bar 422 represents the rub ratio at leading edge 216which is less than the rub ratio of baseline geometry 404 therebyreducing wear to tip portion 210 during a rub event. A middle bar 424represents the rub ratio at mid-chord line 217, and a rightmost bar 426represents the rub ratio at trailing edge 218.

A third group of bars 428 represents the rub ratio for tip portion 210with second tip geometry 408. A leftmost bar 430 represents the rubratio at leading edge 216, a middle bar 432 represents the rub ratio atmid-chord line 217, and a rightmost bar 434 represents the rub ratio attrailing edge 218. At each location, leading edge 216, mid-chord line217, and trailing edge 218, the rub ratio is less than baseline geometry404 thereby reducing wear of tip portion 210 during a rub event.

A fourth group of bars 436 represents the rub ratio for tip portion 210with third tip geometry 410. A leftmost bar 438 represents the rub ratioat leading edge 216, a middle bar 440 represents the rub ratio atmid-chord line 217, and a rightmost bar 442 represents the rub ratio attrailing edge 218. At each location, leading edge 216, mid-chord line217, and trailing edge 218, the rub ratio is lower than baselinegeometry 404 thereby reducing wear of tip portion 210 during a rubevent.

As shown in chart 400, modifying the geometry of tip portion 210 andgrinding an oblique section, such as oblique section 300 and/or 320 intotip portion 210, reduces the wear of rotor blade 200 (shown in FIG. 3)when compared to baseline geometry 404 without the oblique section.Specifically, modifying tip portion 210 geometry reduces the rub ratioof blade 200. For example, oblique section 300 within tip portion 210alters the way in which blade 200 contacts casing 106 during a rubevent. Oblique section 300 lowers the contact force between rotor blade200 and casing 106 thereby reducing vibration and deflection. Byreducing the radial and tangential loads induced into rotor blade 200,vibration is reduced, thereby reducing radial elongation of rotor blade200. Additionally, modifying the geometry of tip portion 210 alsomodifies the vibratory modes that contribute to radial elongation withinblade 200. Reducing radial elongation within rotor blade 200 decreasesthe amount of material loss due to rubbing against casing 106 and thuswear of rotor blade 200. In alternative embodiments, modifying thegeometry of tip portion 210 results in different rub ratio values ofblade 200 then illustrated in chart 400.

In the embodiments described above and referencing FIGS. 1-3, rotorblade 200 is shown and described as a compressor blade. Withincompressor section 104, each compressor stage may incorporate rotorblades 200 that include different oblique sections, such as obliquesections 300 and 320. For example, a first compressor stage includes aplurality of rotor blades 200 with tip portion 210 having obliquesection 300, while a second compressor stage includes a plurality ofrotor blades 200 with tip portion 210 having oblique section 320.Moreover, in alternative embodiments, tip portion 210 having an obliquesection, such as oblique section 300, is in any other blade withinturbomachine 100, such as, turbine section 112.

FIG. 5 is a schematic view of an alternative tip portion 500 for usewith rotor blade 200 (shown in FIG. 2). In this alternative embodiment,rotor blade 200 includes pressure sidewall 212 and an opposing suctionsidewall 214 which extend from root portion 208 to tip portion 500.Additionally, tip portion 500 includes planar section 222 that extendsfrom pressure sidewall 212 to suction sidewall 214 and substantiallyperpendicular thereto. Further, tip portion 500 includes an obliquesection 502 that convexly curves from planar section 222 inward towardsroot portion 208 to leading edge 216 forming a recess 504. Specifically,convex oblique section 502 extends a distance 506 along tip portion 500from leading edge 216 approximately 30% of chord distance 304 of airfoil202. Additionally, convex oblique section 502 extends a depth 508 fromplanar section 222. In alternative embodiments, convex oblique section502 extends for any other distance 506 and/or depth 508 that enablesrotor blade 200 to function as described herein.

Additionally, or alternatively, in this alternative embodiment, tipportion 500 includes oblique section 510 that concavely curves fromplanar section 222 inward towards root portion 208 to trailing edge 218forming a recess 512. Specifically, concave oblique section 510 extendsa distance 514 along tip portion 500 from trailing edge 218approximately 30% of chord distance 304 of airfoil 202. Additionally,concave oblique section 510 extends for depth 508 from planar section222. In alternative embodiments, concave oblique section 510 extends forany other distance 514 and/or depth 508 that enables rotor blade 200 tofunction as described herein. Further, in alternative embodiments,concave oblique section 510 is adjacent to leading edge 216 and/orconvex oblique section 502 is adjacent to trailing edge 218.

Similar to tip portion 210 (shown in FIG. 3), tip portion 500 reducesthe rub ratio of blade 200. Oblique section 502 and/or 510 lowers thecontact force between rotor blade 200 and casing 106 (shown in FIG. 1)thereby reducing radial elongation. Reducing radial elongation withinrotor blade 200 decreases the amount of material loss due to rubbingagainst casing 106 and thus wear of rotor blade 200.

FIG. 6 is a schematic view of another alternative tip portion 600 foruse with rotor blade 200 (shown in FIG. 2). In this alternativeembodiment, rotor blade 200 includes pressure sidewall 212 and anopposing suction sidewall 214 which extend from root portion 208 to tipportion 600. Additionally, tip portion 600 includes a first planarsection 602 and a second planar section 604 that each extend frompressure sidewall 212 to suction sidewall 214 and substantiallyperpendicular thereto. Further, tip portion 600 includes an obliquesection 606 forming a recess 608 between first and second planarsections 602 and 604. Specifically, oblique section 606 extends adistance 610 along tip portion 600 from first planar section 602 tosecond planar section 604 at approximately 40% of chord distance 304 ofairfoil 202 centering about mid-chord line 217. Oblique section 606 hasa first section 612 that extends from first planar section 602 tomid-chord line 217 at a depth 614 such that first section 612 slopesfrom first planar section 602 towards root portion 208 in a directiontowards trailing edge 218. Oblique section 606 has a second section 616that extends from second planar section 604 to mid-chord line 217 suchthat second section 616 slopes from second planar section 604 towardsroot portion 208 in a direction towards leading edge 216. In thisalternative embodiment, oblique section 606 forms a V-shaped recess 608about mid-chord line 217. In alternative embodiments, oblique section606 extends for any other distance 610 and/or depth 614 that enablesrotor blade 200 to function as described herein. Additionally, inalternative embodiments, oblique section 606 does not center aboutmid-chord line 217.

Similar to tip portion 210 (shown in FIG. 3), tip portion 600 reducesthe rub ratio of blade 200. Oblique section 606 lowers the contact forcebetween rotor blade 200 and casing 106 (shown in FIG. 1) therebyreducing radial elongation. Reducing radial elongation within rotorblade 200 decreases the amount of material loss due to rubbing againstcasing 106 and thus wear of rotor blade 200.

FIG. 7 is a schematic view of a further alternative tip portion 700 foruse with rotor blade 200 (shown in FIG. 2). In this alternativeembodiment, rotor blade 200 includes pressure sidewall 212 and anopposing suction sidewall 214 which extend from root portion 208 to tipportion 700. Additionally, tip portion 700 includes a first planarsection 702 and a second planar section 704 that each extend frompressure sidewall 212 to suction sidewall 214 and substantiallyperpendicular thereto. Further, tip portion 700 includes an obliquesection 706 forming a recess 708 between first and second planarsections 702 and 704. Specifically, oblique section 706 extends adistance 710 along tip portion 700 from first planar section 702 tosecond planar section 704 at approximately 40% of chord distance 304 ofairfoil 202 centering about mid-chord line 217. Oblique section 706 hasa first section 712 that extends from first planar section 702 tomid-chord line 217 at a depth 714 such that first section 712 concavelyslopes from first planar section 602 towards root portion 208 in adirection towards trailing edge 218. Oblique section 706 has a secondsection 716 that extends from second planar section 704 to mid-chordline 217 such that second section 716 convexly slopes from second planarsection 704 towards root portion 208 in a direction towards leading edge216. In this alternative embodiment, oblique section 706 forms aU-shaped recess 708 about mid-chord line 217. In alternativeembodiments, oblique section 706 extends for any other distance 710and/or depth 714 that enables rotor blade 200 to function as describedherein. Additionally, in alternative embodiments, oblique section 706does not center about mid-chord line 217.

Similar to tip portion 210 (shown in FIG. 3), tip portion 700 reducesthe rub ratio of blade 200. Oblique section 706 lowers the contact forcebetween rotor blade 200 and casing 106 (shown in FIG. 1) therebyreducing radial elongation. Reducing radial elongation within rotorblade 200 decreases the amount of material loss due to rubbing againstcasing 106 and thus wear of rotor blade 200.

The above described rotor blade tip geometries reduces wear in aturbomachine. Specifically, a rotor blade includes an airfoil having asuction sidewall coupled to a pressure sidewall at a leading edge and atrailing edge. A tip portion extends between the suction sidewall andthe pressure sidewall and includes a planar section and an obliquesection. In some embodiments, the tip portion includes a first obliquesection and a second oblique section. Modifying the rotor blade tipgeometry by grinding the tip portion and forming the oblique sectionreduces the rub ratio of the rotor blade and, thereby, the wear of therotor blade. Specifically, the oblique section is sized such that acontact area between the rotor blade and a surrounding casing isreduced, thereby decreasing the radial and tangential loads induced intothe rotor blade during a rub event. Reducing the loads resulting from arub event decreases vibration and deflection of the rotor blade andreduces material loss at the tip portion. Furthermore, modifying therotor blade tip geometry changes the vibratory modes of the rotor bladesuch that radial elongation is decreased further reducing material lossat the tip portion. Additionally, a reduction in radial deflectionallows the rotor blade to be positioned closer to the surroundingcasing. Accordingly, decreasing the rub ratio of the rotor bladedecreases wear and material loss during a rub event, increasesturbomachine performance, and reduces maintenance costs.

An exemplary technical effect of the methods, systems, and apparatusdescribed herein includes at least one of the following: (a) decreasingmaterial loss of the rotor blade tip during a rub event with asurrounding casing; (b) reducing wear of the rotor blade; (b) decreasinga clearance gap between the rotor blade and the casing; (c) reducingmaintenance costs of turbomachines; and (d) increasing turbomachineperformance.

Exemplary embodiments of methods, systems, and apparatus for reducingrotor blade tip wear are not limited to the specific embodimentsdescribed herein, but rather, components of systems and/or steps of themethods may be utilized independently and separately from othercomponents and/or steps described herein. Further, the methods, systems,and apparatus may also be used in combination with other systemsrequiring decreasing wear from a rub event, and the associated methodsare not limited to practice with only the systems and methods describedherein. Rather, the exemplary embodiment can be implemented and utilizedin connection with many other applications, equipment, and systems thatmay benefit from reducing wear on a blade tip.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. An airfoil for use in a turbomachine, saidairfoil comprising: a pressure sidewall; a suction sidewall coupled tosaid pressure sidewall, wherein said suction sidewall and said pressuresidewall define a leading edge and an opposite trailing edge, whereinsaid leading edge and said trailing edge define a chord distance; a rootportion; and a tip portion extending between said pressure sidewall andsaid suction sidewall such that said tip portion is substantiallyperpendicular to each sidewall, said tip portion comprises at least oneplanar section and at least one oblique section that forms a recesswithin said tip portion, said at least one oblique section extends fromsaid at least one planar section towards said root portion along saidchord distance, said tip portion is configured to reduce airfoil wearduring contact with a surrounding casing, wherein said at least oneoblique section comprises a first oblique section and a second obliquesection, said first oblique section extends convexly from said leadingedge to said at least one planar section and said second oblique sectionextends concavely from said trailing edge to said at least one planarsection.
 2. The airfoil in accordance with claim 1, wherein said atleast one oblique section extends from said leading edge within a rangefrom approximately 5% to approximately 15% of said chord distance tosaid at least one planar section, wherein said leading edge has a firstlength that extends between said root portion and said at least oneoblique section and said trailing edge has a second length that extendsbetween said root portion and said at least one planar section such thatsaid first length is less than said second length, and wherein the atleast one planar section defines a radially outer surface of theairfoil.
 3. The airfoil in accordance with claim 1, wherein said atleast one oblique section extends from said leading edge within a rangefrom approximately 15% to approximately 30% of said chord distance tosaid at least one planar section, wherein said leading edge has a firstlength that extends between said root portion and said at least oneoblique section and said trailing edge has a second length that extendsbetween said root portion and said at least one planar section such thatsaid first length is less than said second length.
 4. The airfoil inaccordance with claim 1, wherein said at least one oblique sectionextends from said leading edge within a range from approximately 30% toapproximately 50% of said chord distance to said at least one planarsection, wherein said leading edge has a first length that extendsbetween said root portion and said at least one oblique section and saidtrailing edge has a second length that extends between said root portionand said at least one planar section such that said first length is lessthan said second length.
 5. The airfoil in accordance with claim 1,wherein said at least one oblique section extends from said trailingedge within a range from approximately 5% to approximately 15% of saidchord distance to said at least one planar section, wherein said leadingedge has a first length that extends between said root portion and saidat least one planar section and said trailing edge has a second lengththat extends between said root portion and said at least one obliquesection such that said first length is greater than said second length.6. The airfoil in accordance with claim 1, wherein said at least oneoblique section extends from said trailing edge within a range fromapproximately 15% to approximately 30% of said chord distance to said atleast one planar section, wherein said leading edge has a first lengththat extends between said root portion and said at least one planarsection and said trailing edge has a second length that extends betweensaid root portion and said at least one oblique section such that saidfirst length is greater than said second length.
 7. The airfoil inaccordance with claim 1, wherein said at least one oblique sectionextends from said trailing edge within a range from approximately 30% toapproximately 50% of said chord distance to said at least one planarsection, wherein said leading edge has a first length that extendsbetween said root portion and said at least one planar section and saidtrailing edge has a second length that extends between said root portionand said at least one oblique section such that said first length isgreater than said second length.
 8. The airfoil in accordance with claim2, wherein said at least one oblique section comprises a first obliquesection and a second oblique section, said first oblique section extendsfrom said leading edge approximately 15% of said chord distance to saidat least one planar section and said second oblique section extends fromsaid trailing edge approximately 15% of said chord distance to said atleast one planar section.
 9. The airfoil in accordance with claim 8, theat least one planar section comprising exactly one planar section, theexactly one planar section extending from the first oblique section tothe second oblique section, wherein said leading edge has a first lengththat extends between said root portion and said first oblique sectionand said trailing edge has a second length that extends between saidroot portion and said second oblique section such that said first lengthis substantially equal to said second length.
 10. The airfoil inaccordance with claim 1, wherein said at least one oblique sectionextends from said at least one planer section towards said root portionwithin a range including approximately 2 mils to less than 5 mils. 11.The airfoil in accordance with claim 1, wherein said at least one planarsection comprises a first planar section adjacent said leading edge anda second planar section adjacent trailing edge, said at least oneoblique section extends between said first planar section and saidsecond planar section.
 12. The airfoil in accordance with claim 9,wherein said at least one oblique section is defined with a convexcurve.
 13. A turbomachine comprising: a casing; a rotor assembly, saidcasing at least partially extending about said rotor assembly, saidrotor assembly comprising: a rotor shaft; a plurality of rotor bladescoupled to said rotor shaft, each rotor blade of said plurality of rotorblades comprises an airfoil comprising a pressure sidewall and a suctionsidewall coupled to said pressure sidewall, wherein said suctionsidewall and said pressure sidewall define a leading edge and anopposite trailing edge, wherein said leading edge and said trailing edgedefine a chord distance, said airfoil further comprising a root portionand a tip portion extending between said pressure sidewall and saidsuction sidewall such that said tip portion is substantiallyperpendicular to each sidewall, said tip portion comprising at least oneplanar section and at least one oblique section that forms a recesswithin said tip portion, said at least one oblique section extends fromsaid at least one planar section towards said root portion along saidchord distance, said tip portion is configured to reduce rotor bladewear during contact with said casing, wherein said at least one obliquesection comprises a first oblique section and a second oblique section,said first oblique section extends convexly from said leading edgeapproximately 15% of said chord distance to said at least one planarsection and said second oblique section extends concavely from saidtrailing edge approximately 15% of said chord distance to said at leastone planar section.
 14. The turbomachine in accordance with claim 13,wherein said at least one oblique section extends from said leading edgeto said at least one planar section, wherein a distance measured betweensaid casing and said leading edge is greater than a distance measuredbetween said casing and said trailing edge, and wherein each rotor bladeof the plurality of rotor blades comprises a turbine rotor blade. 15.The turbomachine in accordance with claim 13, wherein said at least oneoblique section extends from said trailing edge to said at least oneplanar section, wherein a distance measured between said casing and saidtrailing edge is greater than a distance measured between said casingand said leading edge.
 16. A method for reducing blade wear duringturbomachine operation, the turbomachine including a casing, a rotorshaft, and a plurality of rotor blades, each rotor blade of theplurality of rotor blades including an airfoil including a pressuresidewall and a suction sidewall coupled to the pressure sidewall,wherein the suction sidewall and the pressure sidewall define a leadingedge and an opposite trailing edge, wherein the leading edge and thetrailing edge define a chord distance, the airfoil further includes aroot portion and a tip portion extending between the pressure sidewalland the suction sidewall such that the tip portion is substantiallyperpendicular to each sidewall, said method comprising: removing bladematerial from the tip portion comprising forming a recess from at leastone oblique section adjacent at least one planar section on the tipportion, the at least one oblique section extends from the at least oneplanar section towards the root portion along the chord distance; andcoupling the rotor blade to the rotor shaft such that duringturbomachine operation when the tip portion contacts the casing, wear ofthe rotor blade is reduced, wherein the at least one oblique sectionextends from the at least one planar section to at least one of theleading edge and the trailing edge, wherein said at least one obliquesection comprises a first oblique section and a second oblique section,said first oblique section extends convexly from said leading edge tosaid at least one planar section and said second oblique section extendsconcavely from said trailing edge to said at least one planar section.17. The method in accordance with claim 16, wherein removing bladematerial from the tip portion further comprises removing blade materialfrom the tip portion at the leading edge such that the leading edge hasa first length that extends between the root portion and the at leastone oblique section and the trailing edge has a second length thatextends between the root portion and the at least one planar sectionsuch that the first length is less than the second length.
 18. Themethod in accordance with claim 16, wherein removing blade material fromthe tip portion further comprises removing blade material from the tipportion at the trailing edge such that the leading edge has a firstlength that extends between the root portion and the at least one planarsection and the trailing edge has a second length that extends betweenthe root portion and the at least one oblique section such that thefirst length is greater than the second length, and wherein the recessis not centered about a mid-chord line.
 19. The method in accordancewith claim 16, wherein removing blade material from the tip portionfurther comprises: removing the leading edge tip portion via a grindingprocess to form a first oblique section; and removing the trailing edgetip portion via a grinding process to form a second oblique section.